Hi Kevin,
>topic 3: DataReferenceImpl
>
>I would like to create a line with one anchored point *and of constant
>length*, basically a ray which the user can grab the outer end to trace a
>circle.
>
>The only examples I have seen so far are a line which uses one "northing"
>point (Ugo's example in Section 6.4) and a line defined by two moveable points.
>
>Can I create such a line as described?
Here is a short program demonstrating what you want.
-Curtis
--
// AnchoredPoint.java
import visad.*;
import visad.java3d.*;
import visad.util.Util;
import java.rmi.RemoteException;
import javax.swing.*;
public class AnchoredPoint {
private static final float LENGTH = 5;
private static final float END_X = 2;
private static final float END_Y = 3;
public static void main(String[] args) throws Exception {
// math types
RealType x = RealType.getRealType("x");
RealType y = RealType.getRealType("y");
final RealTupleType xy = new RealTupleType(x, y);
// mappings
ScalarMap xmap = new ScalarMap(x, Display.XAxis);
ScalarMap ymap = new ScalarMap(y, Display.YAxis);
xmap.setRange(END_X - LENGTH, END_X + LENGTH);
ymap.setRange(END_Y - LENGTH, END_Y + LENGTH);
// display
DisplayImpl display = new DisplayImplJ3D("display",
new TwoDDisplayRendererJ3D());
display.disableAction();
display.addMap(xmap);
display.addMap(ymap);
GraphicsModeControl gmc = display.getGraphicsModeControl();
gmc.setScaleEnable(true);
gmc.setPointSize(5.0f);
// data references
final DataReferenceImpl line_ref = new DataReferenceImpl("line");
final DataReferenceImpl pt_ref = new DataReferenceImpl("point");
display.addReference(line_ref);
display.addReferences(new DirectManipulationRendererJ3D(), pt_ref, null);
// data objects
doPoint(xy, 0, 0, pt_ref);
doLine(xy, 0, 0, line_ref);
// computational cell
CellImpl cell = new CellImpl() {
public void doAction() {
// get point coordinates
RealTuple tuple = (RealTuple) pt_ref.getData();
if (tuple == null) return;
double[] vals = tuple.getValues();
float xval = (float) vals[0];
float yval = (float) vals[1];
// adjust point coordinates
float xlen = END_X - xval;
float ylen = END_Y - yval;
float len = (float) Math.sqrt(xlen * xlen + ylen * ylen);
if (!Util.isApproximatelyEqual(len, LENGTH)) {
double lamda = LENGTH / len;
xval = (float) (END_X + lamda * (xval - END_X));
yval = (float) (END_Y + lamda * (yval - END_Y));
try { doPoint(xy, xval, yval, pt_ref); }
catch (Exception exc) { exc.printStackTrace(); }
return; // point change will retrigger cell
}
// update line
try { doLine(xy, xval, yval, line_ref); }
catch (Exception exc) { exc.printStackTrace(); }
}
};
cell.addReference(pt_ref);
display.enableAction();
// show display onscreen
JFrame frame = new JFrame("Fixed-length line with one anchored point");
JPanel p = new JPanel();
p.setLayout(new BoxLayout(p, BoxLayout.X_AXIS));
p.add(display.getComponent());
frame.setContentPane(p);
frame.setSize(400, 400);
Util.centerWindow(frame);
frame.show();
}
private static void doLine(RealTupleType rtt, float x, float y,
DataReferenceImpl line_ref) throws VisADException, RemoteException
{
float[][] samples = { {x, END_X}, {y, END_Y} };
Gridded2DSet set = new Gridded2DSet(rtt, samples, 2);
line_ref.setData(set);
}
private static void doPoint(RealTupleType rtt, float x, float y,
DataReferenceImpl pt_ref) throws VisADException, RemoteException
{
pt_ref.setData(new RealTuple(rtt, new double[] {x, y}));
}
}
